Instead of modeling the kernel-tools build after the bootstrap tools, build

kernel tools the way cross-tools get built.  This seems to result in the
tool getting installed in the right place.  It also seems more correct in
retrospect, because if a tool emitted code or binary data as part of
building the kernel, it should do so in target-specific ways (endianess,
architecture, whatever).  That issue is moot for aicasm, our only current
tool, but it still seems to be more correct in principle.

Makefile.inc1

@@ -439,16 +439,6 @@ IMAKE_MTREE=	MTREE_CMD="nmtree ${MTREEFLAGS}"
 KMAKEENV=	${WMAKEENV}
 KMAKE=		${KMAKEENV} ${MAKE} ${.MAKEFLAGS} ${KERNEL_FLAGS} KERNEL=${INSTKERNNAME}
 
-# kernel build-tools stage
-KTMAKE=		MAKEOBJDIRPREFIX=${WORLDTMP} \
-		${WMAKEENV} ${MAKE} -f Makefile.inc1 \
-		TARGET=${TARGET} TARGET_ARCH=${TARGET_ARCH} \
-		DESTDIR= \
-		BOOTSTRAPPING=${OSRELDATE} \
-		SSP_CFLAGS= \
-		-DNO_LINT \
-		-DNO_CPU_CFLAGS -DNO_WARNS -DNO_CTF -DEARLY_BUILD
-
 #
 # buildworld
 #
@@ -1029,7 +1019,7 @@ buildkernel:
 	@echo "--------------------------------------------------------------"
 	@echo ">>> stage 2.3: build tools"
 	@echo "--------------------------------------------------------------"
-	${_+_}cd ${.CURDIR}; ${KTMAKE} kernel-tools
+	${_+_}cd ${.CURDIR}; ${XMAKE} kernel-tools
 .if !defined(NO_KERNELDEPEND)
 	@echo
 	@echo "--------------------------------------------------------------"
@@ -1360,9 +1350,9 @@ build-tools: .MAKE
 # kernel-tools: Build kernel-building tools
 #
 kernel-tools: .MAKE
-	mkdir -p ${WORLDTMP}/usr
+	mkdir -p ${MAKEOBJDIRPREFIX}/usr
 	mtree -deU -f ${.CURDIR}/etc/mtree/BSD.usr.dist \
-	    -p ${WORLDTMP}/usr >/dev/null
+	    -p ${MAKEOBJDIRPREFIX}/usr >/dev/null
 .for _tool in \
     sys/dev/aic7xxx/aicasm
 	${_+_}@${ECHODIR} "===> ${_tool} (obj,depend,all,install)"; \
@@ -1370,7 +1360,7 @@ kernel-tools: .MAKE
 		${MAKE} DIRPRFX=${_tool}/ obj && \
 		${MAKE} DIRPRFX=${_tool}/ depend && \
 		${MAKE} DIRPRFX=${_tool}/ all && \
-		${MAKE} DIRPRFX=${_tool}/ DESTDIR=${WORLDTMP} install
+		${MAKE} DIRPRFX=${_tool}/ DESTDIR=${MAKEOBJDIRPREFIX} install
 .endfor
 
 #